A practical method for utilization of commercial cyclic testing apparatuses for computation of site response in central Adapazari

Yılmaz, Mustafa Tolga
Zehtab, Kaveh Hassan
We suggest a practical method for estimating strain-modulus-damping relationships for utilization in equivalent-linear site response analyses, so that the necessity for more sophisticated sampling and testing procedures can be justified. The method employs the commercial cyclic testing apparatuses, which have limitations in low-strain ranges, and the in-situ seismic tests. The shear modulus at about 1% cyclic shear strain amplitude and the shear-wave velocity measured in-situ is used for building a hyperbolic relationship between shear stress and shear strain. An extension of Masing's rule and the constraint on hysteretic damping at 1% cyclic shear strain amplitude leads to a strain-damping relationship. By putting a particular emphasis on the soils of Adapazari, a city famous for the concentrated damage on alluvium basin during the 1999 Kocaeli (Mw7.4) earthquake, we demonstrated the usefulness of the method, and concluded that the shear-modulus reduction and damping characteristics of Adapazari soils can yield to site amplification factors greater than those predicted by strain-modulus-damping relationships presented in literature, and can more efficiently explain the concentration of damage on the alluvium basin. Through the comparisons of spectral amplification factors computed by equivalent-linear site response analyses, we justified the necessity to run a more sophisticated testing program on determination of cyclic stress-strain behavior of Adapazari soils, and consequently to consider transient nonlinear site-response analyses in order to reduce the possible bias in calculation of spectral amplification factors.